Radar image display

ABSTRACT

A method is provided that facilitates generating a radar image to be displayed by a radar system. The method includes receiving range data and azimuth data carried by a radar signal transmitted from a radar antenna in communication with the radar system, wherein the range data and the azimuth data represent the radar image as a plurality of azimuth segments that collectively form the radar image in a polar coordinate system. The range data and the azimuth data are translated into abscissa data and ordinate data that represent the radar image in a Cartesian coordinate system, and noise is filtered from the radar image, followed by generation of the radar image including the target to be displayed by a display screen to an operator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.K. Patent Application No.GB0719880.7, filed Oct. 12, 2007, the entirety of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates generally to an improved radar processingmethod and system, and more specifically to radar imaging and targetidentification, and in particular to a method and apparatus forimproving the representation of targets within radar images.

2. Description of Related Art

Radar is the primary airspace sensor for ground-based, marine andairborne surveillance and monitoring applications. Its use within bothcommercial and military environments is widely known, and to date itremains the most effective technique for identifying targets within anarea of interest.

Conventional radar display systems have historically been based oncylindrical cathode ray tube (CRT) arrangements, in which a phosphorscreen is excited by a sweeping beam that is synchronised with therotation of the radar antenna. Any target objects within the monitoredarea give rise to a return (i.e. reflected) radio signal that appears asa ‘blip’ (e.g. a bright spot/area) on the radar image display. This kindof display is usually referred to as a plan position indicator (PPI),which functions as a range and azimuth map centered on a polarcoordinate system. Since the phosphor typically has a long persistence,a target signal will remain visible for several rotations or scans ofthe sweeping beam. Thus, moving targets are found to leave a visibletrail of decayed images on the image display. In this way, the positionand velocity of a target can be reliably monitored, allowing an operatorto determine the direction in which a target is heading.

Despite the large number of CRT radar display systems that remain inexistence, more recent implementations have begun to make use ofcomputer-based technologies and software in order to replace and/orupgrade the more historical image displays. For instance, many modernradar display systems have been implemented within computer workstationenvironments, in which a radar signal feed is passed to the workstationfor display to an operator as a series of real-time radar images. Theimages are typically displayed via the workstation's monitor, which maybe a conventional VDU, TFT or LCD style display device.

In order to successfully implement a radar display system within aworkstation environment a large degree of data processing is typicallyrequired. Most radar signal feeds are analogue in nature, so it is usualto convert the feed to digital form via an analogue-to-digitalconverter. The digital radar data is then conventionally processed via a‘Radar Scan Converter’ (RSC) that converts the range and azimuth datafrom a polar coordinate system into a dataset based on rectangular (i.e.Cartesian) coordinates for real-time display on the workstation'smonitor.

However, a potential drawback of many such implementations is that theamount of processing power required to perform the digitization and/orconversion is relatively high, which consequently places significantdemands on the workstation's CPU and associated memory. In some cases,the CPU demands may be so great that this introduces a significant delayinto the image processing, such that the displayed image lags behind theradar signal feed, which is obviously undesirable within most radarapplications. To a limited degree, the art has addressed this problem byattempting to ‘load-balance’ the processing requirements between the CPUand the processing elements on the workstation's graphics card. However,in nearly all cases, such implementations have fallen significantlyshort of removing the processing burden from the CPU. Therefore, todate, most of the known computer-based implementations of radar displaysystems are highly CPU intensive.

Computer-based implementations offer significant flexibility andscalability in controlling the display of radar images. Many of theknown workstation implementations provide radar images which offerconsiderably better rendered detail than conventional CRT displays.However, it is usually the case that existing techniques used to processthe radar images generally do not make best use of the available dataand, in particular, are not especially suited to mitigate against theeffects of noise within the radar images. Therefore, the representationof targets within a displayed image may not match those that aretheoretically possible given the power and/or resolution of the radardisplay system.

The present invention seeks to provide a much improved and less CPUintensive method for displaying radar images, so as to enhance theidentification and representation of targets by processing the images toextract the maximum amount of information from the radar signal andminimize, or substantially eliminate, sources of background noise.

BRIEF SUMMARY

According to one aspect, the subject application involves a computerimplemented method for improving the representation of targets withinradar images, including the steps of receiving input data comprising atleast one radar image; dividing the image into a plurality of radialcomponents; and applying a filtering means to at least two adjacentradial components to thereby reduce noise in the return signals from anytarget present within those components.

The method of the present invention is preferably implemented within aconventional computer workstation environment. However, it is to beappreciated that any other suitable computing platform or server rackarrangement may alternatively be used without sacrificing any of theadvantages of the invention. In preferred arrangements, the method isimplemented within the graphics processing environment of theworkstation and makes use of the graphics processing architecture andgraphics programmable pipeline (as discussed in greater detail later).By implementing the present method within a graphics processingenvironment, the radar display system advantageously becomes independentof the processing platform and is no longer limited to any particularoperating system. Therefore, the present method is both platform andoperating system independent. Moreover, as the implementation makes useof industry standard specifications for cross-language, cross-platformgraphics APIs (Application Programming Interfaces) the invention is notlimited to specific graphics architectures and therefore may beimplemented on any existing or future graphics hardware that supportsthe standard specifications.

The radar signal feed may be received as an analogue input data andtherefore a conversion step may be applied to the feed so as to convertthe analogue data into digital form. The conversion step may involve theapplication of a conventional analogue-to-digital converter and possiblymultiplexing stages, so as to preferably generate a 2-dimensionalpixelated image. Alternatively, the radar signal feed may be received asa digital data stream, with the conversion being performed within theradar receiver circuitry.

The radar images are passed to the computer workstation, or possibly toa network of workstations etc., for image processing to be performed.The image data is preferably received within the workstation's graphicsprocessing environment (GPE) where filtering of the images can becarried out. The GPE is also preferably responsible for the display ofthe radar image data, which is discussed in greater detail later.

To process the radar images, each image is preferably converted into anarray of data lines, commonly referred to as a ‘polar store’. The arraymay be a memory store preferably maintained in graphics memory, intowhich the converted radar data is placed for subsequent processing.According to the present method, a radar image is divided (e.g.dissected) into a plurality of radial components which are thenconverted into data lines within the array. As the radar image data isconventionally based on a polar coordinate system, a polar-Cartesiancoordinate transformation may be applied to each radial component duringconversion into the array. Any suitable conversionfunction/algorithm/matrix may be used to effect the coordinatetransformation, as commonly known in the art.

References herein to ‘radial components’ are intended to refer to theazimuths or linear scan elements within the image space which whenarranged radially and azimuthally around the point of origin make up therespective 2-dimensional radar images. In a physical sense therefore,each azimuth corresponds to the narrow scan volume that is swept out bythe finite width of the radar beam as it rotates about the point oforigin. Hence, each azimuth contains the radar signal data that wasreturned by way of reflection from any targets or other objects (e.g.land masses etc.) within that scan volume.

As the angular extent of each azimuth is defined by the width of theradar beam, it is easy to appreciate that there may be a very largenumber of azimuths within each 360 degrees of rotation, depending uponthe resolution of the radar antenna and other characteristics of theradar system.

By ‘point of origin’ we mean the location at which the radar beamoriginates, which in most cases will correspond to the site of theantenna. Evidently, this point will usually also serve to define theorigin of the polar coordinate system in the radar images.

The use of a polar store greatly facilitates simplified processing ofthe radar image data and allows any number of different processing, andin particular, filtering algorithms to be applied to the data to improveand enhance the display of radar images to an operator.

In accordance with the present invention, the provision of a filteringmeans that is applied to at least two adjacent radial componentsachieves a ‘cross-azimuth’ filtering effect that is able to take intoconsideration the respective contributions of the return signals fromany target or targets found to be present within those azimuths. Hence,the data lines in the array that correspond to those azimuths can bemanipulated via appropriate filtering algorithms to make best use of theavailable data, so as to provide improved radar images and better targetrendition.

A target within a radar image will typically extend across severalazimuths, unless it is extremely small in nature or else has arelatively compact cross-section as viewed along the radial direction.Therefore, a return signal (i.e. a reflected radar pulse) will bepresent in each of the azimuths across which the target extends.Depending upon the degree to which the radar pulse is reflected, as itsweeps the width of the target, the return signals will vary inintensity between adjacent azimuths. Hence, by performing across-azimuth filtering across those azimuths, it is possible toeffectively combine the respective contributions of each of the returnsignals, which is found to significantly improve the overall returnsignal and mitigate against background noise. Thus, a much betterrepresentation of the target may be reproduced within the radar image,while consequently improving the signal-to-noise ratio over thebackground.

The filtering means preferably comprises a filter function that mayserve as a convolution style filter that can be applied to the returnsignals in those azimuths across which the target resides. In oneembodiment, the filter function may be a substantially Gaussian-shapedconvolution filter that is convolved with the return signals to giverise to a better representation of the target within the radar image.This result arises from the fact that the intensity of the returnsignals between the adjacent azimuths will generally vary according to aGaussian function. Therefore, the convolution of the return signals witha Gaussian-shaped convolution filter will result in better targetdefinition, which thereby improves the rendering of the target whendisplayed in the radar image.

It is found that a more clearly rendered target enhances identificationand may also assist an operator with the quantification of the target'sspeed and direction throughout successive beam rotations. Hence, thepre-processing step played by the convolution is found to aid automatictarget identification routines by providing a more consistently resolvedset of targets.

It is to be appreciated however, that any generic convolution stylefilter may be used in accordance with the present invention, whetherGaussian or some other form of geometric function depending upon theparticular application and image processing requirements. Theconvolution filter coefficients may be selected so as to be rangedependent to thereby better reflect the characteristics of the actualdata. Moreover, any other filtering techniques may also be applied withor without convolution, consistent with any of the embodiments describedherein, including edge enhancers, noise spike rejecters, noise reducers,signal boosters and localized signal thresholds. Each of which leadingto an improved representation of data and enhanced target rendition.

Each data line in the polar store preferably comprises a plurality ofindividual data elements arranged in order of ascending range (i.e.increasing from the point of origin). Each data element will thereforehave a value that is indicative of the intensity of any return signal atthat range. During the conversion of the radar image into radialcomponents, and hence into corresponding data lines within the array,the conversion step preferably applies a mapping function that maps eachpixel within the 2-dimensional radar image to a respective data elementin one or more of the data lines. Since targets will generally extendacross several azimuths (as discussed above), any particular pixel inthe image may therefore be associated with one or more data elements inthe array.

The cross-azimuth filtering methodology of the present invention is ableto make use of this pixel mapping by applying any number of differentfiltering algorithms to the values of the data elements associated witha particular level. Hence, not only may convolution style filters beapplied to the data, but any other additional or alternative filtersteps may also be invoked in accordance with the method of the presentinvention.

In particularly preferred embodiments, the cross-azimuth filtering maycomprise both an ‘azimuth filter’ and a ‘highest wins’ filter applied incombination to improve and enhance the displayed radar image. Herein an‘azimuth filter’ is intended to refer to any generic convolution stylefilter that serves as a prescribed filter function for convolving withthe radar image data, as discussed in detail earlier. The ‘highest wins’filter of the present invention makes use of the multi-element pixelmapping that arises from the conversion of the radar image into thepolar store. In one example, this filter operates by identifying thehighest value from among each of the values of data elements associatedwith a particular pixel and consequently assigns the highest value tothat pixel. In this way, any return signal may be effectively‘strengthened’ by representing the corresponding target by the highestavailable pixel value, thereby improving its apparent significance andvisual impact within the displayed radar image.

This particular filtering technique is especially useful for preservingweaker return signals and for better distinguishing the signal from thebackground noise. Hence, by way of a ‘highest wins’ filter therepresentation of a target can be markedly improved within the displayedimage, which may assist with easier identification and subsequenttrajectory estimation.

It is to be appreciated that the particular filter or filter combinationused in processing the radar images, will depend largely on thecharacteristics of the radar system from which the images are derived.Therefore, if we are only concerned with relatively large targets (i.e.ones which give rise to return signals across multiple azimuths andacross varying range), then an azimuth filter only may be used. However,if it is desired to preserve weaker signals as well, a highest winsfilter may alternatively be applied in isolation or in combination withone or more azimuth filters etc. In most cases, the filter parametersand coefficients may be matched to the characteristics of the returnsignals.

Hence, it is evident that the method of the present invention is able tomake best use of the image data by applying innovative filters andfilter combinations, so as to improve the representation of targets inradar images and reduce the effects of background noise.

The implementation of the present method within a graphics processingenvironment is particularly advantageous, since as we have seen, a highdegree of platform and operating system independence may be achieved.However, in addition to this, significant improvements in processingspeed may be arrived at by making use of the workstation's graphicsprocessing architecture. Most workstations, particularly those of anIBM-compatible personal computer type, contain dedicated video graphicscards that are either integrated into the motherboard or else connect tothe motherboard via industry standard interfaces (e.g. PCl, PCl-Expressand AGP etc.). To control the output of the graphics card, a graphicspipeline is used to instruct the card to perform various renderingoperations. However, modern cards support programmable pipelines thatallow the processing architecture to be controlled via code thatconforms to a prescribed standard library specification.

The method of the present invention is preferably implemented on aprogrammable pipeline graphics card, that enables full optimisation ofthe filtering paradigm and alleviates the processing burden on theworkstation's CPU. In preferred embodiments, the filtering means may beimplemented as a set of programmable instructions, that may be in theform of a ‘shader’ operation. A ‘shader’ is the commonly used term for aset of software instructions that constitute part of the graphicspipeline. Conventional graphics card usually include a GraphicsProcessing Unit (GPU) that accept and execute the instructions of theshader, and therefore it is possible to control the operation of the GPUvia one or more shaders.

Each of the filters of the present invention may be implemented asseparate or combined shader operations for execution on the GPU toprocess the radar image data. Any of the industry standardspecifications may be used in accordance with the invention, including,but not limited to, OpenGL and DirectX. However, it should beappreciated that shader operations are only supported in OpenGL 1.5 andabove and DirectX 8 and later versions. The currently preferredimplementation makes use of the GLSL Shader Language according to thestandard OpenGL 2.0 specification.

In preferred embodiments, the filtering means are implemented accordingto the OpenGL specification and make use of the associated shaderlanguage, OpenGL Shading language (GLSL). In this way, the filtershaders may be used on any workstation that has a graphics processingarchitecture that supports GLSL. Of course, the present method mayalternatively be implemented according to the DirectX specification orother proprietary languages, such as Cg developed by NVidia etc.depending on the graphics architecture and the supported graphicsstandards.

An advantage of implementing the present method within the graphicsprocessing environment of the workstation is that the processing demandson the CPU are dramatically reduced. As most modern GPU architecturescorrespond approximately to an integrated parallel processing device,the speed of the image processing can be significantly increased overthat of a CPU performing the same task. Since the CPU is released fromthe need to carry out processing of the radar images, it can divert itsattention to other operations, so as to avoid any significant drop inthe performance of the workstation as experienced by the operator.

The greater speed of the GPU means that the radar images may bedisplayed in real-time, without introducing any significant delay or lagbetween the output of the images and the radar signal feed.

To further improve the performance of the workstation, additionalprocessing steps may be implemented on the GPU, in preference to theCPU. Therefore, the polar store conversion and coordinate transformationmay all be executed on the GPU via appropriate pipeline operations,which thereby avoids burdening the CPU with relatively highcomputationally intensive tasks.

Although the above embodiments implement the present method in softwarewithin a graphics processing environment, it should be appreciated thatany of the conversion, transformation, filtering and display steps mayalternatively and/or additionally be implemented within hardware on thevideo graphics card or other component of the graphics architecture.Therefore, the present invention also relates to a video graphics cardthat includes a controller, such as a GPU, that is configured viasoftware and/or hardware to implement the steps of the method as set outin any of the disclosed embodiments. The video graphics card may conformto any industry standard interface, such as PCI, PCI-Express or AGP etc.

It should also be noted that the present method may alternatively beimplemented within a graphics environment that is integrated with themotherboard of the workstation, or within any shared graphicsarrangements (e.g. where the GPU makes use of the workstation's RAM orother resources), without sacrificing any of the advantages of theinvention.

The benefits of implementing a radar image display on a computerworkstation having a modern graphics processing environment is that theoutput images may be manipulated and controlled to achieve any number ofvisual display effects in numerous different output modes. Hence, forexample, the output images may be manipulated by an operator to changethe projected viewing angle of the image, so that instead of a purely2-dimensional view (i.e. as seen from above), the radar image may beviewed at an oblique angle to give some perception of depth.

In accordance with the present invention therefore, a number of imagemanipulation and display algorithms may be incorporated within thegraphics processing environment to enable an operator to invoke variousvisual effects in the output radar images. Hence, in a preferredembodiment, a graphical user interface (GUI) may be provided on theoperator's workstation that allows the operator to achieve anyone ormore of the following visualizations and/or effects: to re-size and/ormanually position the display windows within the display environment inreal-time, to have one or multiple display windows simultaneouslyvisible to an operator, to select particular areas of interest withinthe images for further scrutiny, to zoom in/out within the images toenlarge/decrease the size of target profiles, to alter the viewing anglewithin the image and change the projection attributes, to representtargets as 3-dimensional objects, to overlay grids or other projections,to display track information for specific objects, to apply any desiredgrey scale or color palettes for false color display and to merge two ormore images.

It should be appreciated that any of the above visualizations or effectsmay be performed while the radar image data is being updated, so thatimage manipulation can occur simultaneously with ‘live’ (i.e. real-time)updates. For example, a displayed image may be resized while the imageis being updated. In this way, no loss of information occurs while thedata is being actively rendered to the display. As a result, anyprotracted delay in updating the images can thereby be avoided even whenan operator requests some change in the display function.

In addition, any desired underlay image may also be merged with theoverlying radar image to enable coastlines, runways, buildings or anyother structures to be displayed along with the target objects.

It is to be understood that anyone or more of the image manipulationand/or display algorithms may be implemented as a shader operation.Hence, for instance, false color radar images may be generated by way ofan appropriate shader that controls the color of each pixel as afunction of the pixel's properties, e.g. value, position within imageetc. As a result, the graphics pipeline can be controlled to display aradar image according to any desired color scheme or display mode,thereby permitting a large number of different visualizations of thedata.

A shader operation may also be used to implement a ‘fading’ visualeffect in the displayed radar image to emulate the persistence of thephosphor screen in historical radar displays (as discussed earlier).This fading effect is favoured by many operators and consequently it isdesirable to preserve this effect, as it is generally useful fordetermining a target's motion and velocity. Thus, in accordance with thepresent invention, a fading effect may be achieved by way of a shaderthat is implemented within the graphics pipeline that creates theimpression that the workstation display screen has some degree ofpersistence. In other words, the GPU can render images so that theyemulate the effect of a decaying target within a CRT phosphor screen.The shader can therefore be programmed to control the intensity of eachpixel to generate a fading effect within successive images by reducingthe values of the pixels associated with a particular target accordingto an appropriate decay function. In this way, a target may then giverise to a perceptible trail within the radar images that enables anoperator to estimate the heading and velocity of the target.

Any suitable function may be used to control the intensities of thepixels in the images, which in preferred arrangements correspondssubstantially to an exponential decay function.

The time taken for a decaying target trail to fade within successiveimages may be controlled by the shader, so that a gradual shading effectsimilar to that of a CRT phosphor screen may be produced. An optimumfade time is preferably within the range of 1 to 2 minutes, but may beshorter or longer depending on the particular application and desiredfading effect.

It is to be appreciated however that any suitable fading technique maybe used in accordance with the present effect, including, but notlimited to, layered lighting effects as used in standard gaming engines,e.g. ‘spiral staircase’ effects.

Although the present invention is ideally suited for enhancing thevisualization of radar images, and in particular, for improving therepresentation of targets while reducing background noise, it will berecognized that one or more of the principles of the invention couldalso be used in other image processing applications where there is arequirement to augment the representation of objects within images bymitigating against the effects of noise.

According to another aspect, the present application involves a methodof generating a radar image to be displayed by a radar system. Themethod includes receiving range data and azimuth data carried by a radarsignal transmitted from a radar antenna in communication with the radarsystem, wherein the range data and the azimuth data represent the radarimage as a plurality of azimuth segments that collectively form theradar image in a polar coordinate system. The range data and the azimuthdata are translated into abscissa data and ordinate data that representthe radar image in a Cartesian coordinate system, and noise is filteredfrom the radar image by:

-   -   utilizing a return signal contribution reflected by a target        from at least two immediately-adjacent azimuth segments to        render a representation of the target in the radar image,    -   selecting a highest pixel value from a plurality of different        pixel values assigned to be displayed by a common pixel of a        radar display to be displayed by the common pixel, or    -   a combination of both utilizing the return signal contribution        reflected by the target from the at least two        immediately-adjacent azimuth segments and selecting the highest        pixel value from the plurality of different pixel values        assigned to the common pixel to render the representation of the        target to be included as a portion of the radar image to be        displayed.

The radar image is generated and includes the target to be displayed bya display screen to an operator.

According to such a method, the radar signal feed can be converted froman analog signal to a digital signal. Converting the radar signal to adigital signal can be performed by an analog-to-digital converterprovided to a graphics processing unit of the radar system independentof a central processing unit for controlling general operation of theradar system as a whole.

Translating the range data and the azimuth data into abscissa data andordinate data, filtering the noise from the radar image, or bothtranslating the range data and the azimuth data into abscissa data andordinate data, and filtering the noise from the radar image canoptionally be performed by a graphics processing unit of the radarsystem independent of a central processing unit for controlling generaloperation of the radar system as a whole.

One of translating the range data and the azimuth data and filtering thenoise from the radar image can optionally be performed by a graphicsprocessing unit of the radar system independent of a central processingunit for controlling general operation of the radar system as a whole,and another of translating the range data and the azimuth data andfiltering the noise from the radar image is performed by a differentprocessing unit provided to the radar system. The different processingunit can be the central processing unit of the workstation forcontrolling general operation of the radar system as a whole, or atleast controlling general the general flow of information among, andoptionally operation of the workstation components.

The radar image can be communicated over a communication network such asthe Internet, an Intranet, or any other suitable communication networkwith which the workstation is in communication to be displayed by thedisplay screen.

When the radar image is to be displayed, a point of view of the radarimage to be displayed by the display screen can be manipulated in atleast one of a first dimension and a second dimension responsive toreceiving an input from the operator indicating a desired viewpoint ofthe radar image. Thus, radar image presented by the display screen canhave the point of view of looking directly, straight down onto thetarget. Such a manipulation can be considered analogous to a keystonecorrection effect as is known in the art. To so manipulate the point ofview includes adjusting an orientation of the radar image in a thirddimension. Alternately, or in combination, manipulating the point ofview of the radar image optionally further includes conducting ageometric distortion to maintain substantially-overhead point of view ofthe radar image subsequent to manipulating the point of view.

Targets depicted in the radar image can be displayed as a graphicaldepiction of the target in real time by pixels of the display screen.The intensity of these pixels can optionally be gradually faded toemulate a persistence of phosphor of a cathode-ray-tube display screen.Gradually fading the intensity of the target in the radar image can becontrolled by a graphics processing unit of the radar system independentof a central processing unit for controlling general operation of theradar system as a whole.

According to another aspect, a plurality of the azimuth segmentscollectively forming the radar image can be selected to overlap suchthat each overlapping azimuth segment detects a target in a common,overlapping region. Filtering noise from the radar image can optionallyinclude comparing a return signal contribution reflected from the commonregion for each overlapping azimuth segment, and generating the radarimage to include the target within the common region if each returnsignal contribution is indicative of a presence of the target within thecommon region.

According to another aspect, a physical computer-readable medium can beprovided to store computer-executable instructions for performing any ofthe method steps disclosed herein.

The above summary presents a simplified summary in order to provide abasic understanding of some aspects of the systems and/or methodsdiscussed herein. This summary is not an extensive overview of thesystems and/or methods discussed herein. It is not intended to identifykey/critical elements or to delineate the scope of such systems and/ormethods. Its sole purpose is to present some concepts in a simplifiedform as a prelude to the more detailed description that is presentedlater.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, embodiments of which will be described in detail in thisspecification and illustrated in the accompanying drawings which form apart hereof and wherein:

FIG. 1 is a schematic representation of a preferred implementation of aradar display system operating in accordance with an embodiment of amethod of the present invention;

FIG. 2 is an example screenshot of a radar image generated by the radardisplay system of FIG. 1;

FIG. 3 is an example screenshot of another radar image generatedaccording to a different display mode of the radar display system ofFIG. 1, wherein the point of view of the radar image from theperspective of the observer has been manipulated;

FIG. 4 is an example screenshot of another radar image generatedaccording to a different display mode of the radar display system ofFIG. 1, wherein a plurality of windows are simultaneously displayed bythe display screen, and each window includes a different display mode ofthe radar image;

FIG. 5 is an example screenshot illustrating a 3-dimensional close-up oftargets within the radar image of FIG. 3, wherein each target includes adepth dimension; and

FIG. 6 is an example screenshot illustrating trailing target imagesaccording to an aspect of the present invention, wherein each targetincludes a gradually fading tail displayed by gradually fading theintensity of pixels along a path traveled by the target to emulate apersistence of phosphor of a cathode-ray-tube display screen.

DETAILED DESCRIPTION

Certain terminology is used herein for convenience only and is not to betaken as a limitation on the present invention. Relative language usedherein is best understood with reference to the drawings, in which likenumerals are used to identify like or similar items. Further, in thedrawings, certain features may be shown in somewhat schematic form.

It is also to be noted that the phrase “at least one of”, if usedherein, followed by a plurality of members herein means one of themembers, or a combination of more than one of the members. For example,the phrase “at least one of a first widget and a second widget” means inthe present application: the first widget, the second widget, or thefirst widget and the second widget. Likewise, “at least one of a firstwidget, a second widget and a third widget” means in the presentapplication: the first widget, the second widget, the third widget, thefirst widget and the second widget, the first widget and the thirdwidget, the second widget and the third widget, or the first widget andthe second widget and the third widget.

Referring to FIG. 1, there is shown a preferred implementation of aradar display system 10 operating in accordance with the method of thepresent invention. The radar display system 10 comprises a scanningradar antenna 12 of conventional design sited at a location at which thesurrounding area is to be monitored, e.g. at an airfield, at a sea-portor in a battlefield etc. The antenna 12 provides a radar signal feed(indicated by the solid arrow) as an input to a computer workstation 14having an associated TFT display monitor 16 and input device 18, whichin this example is a standard keyboard and mouse.

The computer workstation 14 is an IBM-compatible personal computerarranged in a conventional desktop configuration. In order to convertthe analogue radar signal feed into a digital signal suitable for theworkstation 14, an analogue-to-digital converter (ADC) 20 is provided,as known in the art. In the example of FIG. 1, the ADC 20 is connectedas a peripheral unit, external to the workstation 14. However, in otherexamples, the ADC 20 could be connected as an expansion card within theworkstation 14.

It is also possible, in other examples, to have a customized card thatcan perform each of the capture, conversion, filtering and displayfunctions on its own. In this way, both the acquisition and displayprocessing can be accomplished on a single, self-contained, peripheralcomponent.

The workstation 14 includes both a CPU 22 and a graphics processingenvironment comprising a video graphics card 24 with a GPU 26. Thegraphics card 24 also has an associated graphics memory 28. In theexample of FIG. 1, the graphics card 24 has a GPU 26 that is based on aNvidia chipset which has a graphics pipeline that can be programmedaccording to the OpenGL 2.0 Shading Language (GLSL) standardspecification. This permits the pipeline to be controlled via speciallywritten shader operations.

The graphics card 24 is connected to the motherboard (not shown) of theworkstation 14 via an industry standard PCI-Express peripheral interfaceand provides an output VGA signal to the display monitor 16. An operatoris able to view the radar images in real-time on the monitor 16 and mayperform a number of different visualizations, as will be discussed laterwith reference to FIGS. 2 to 6.

In the example of FIG. 1, the GPU 26 has been programmed to convert thedigitised radar images into a rectangular array of data, i.e. a polarstore, by dividing each image into a plurality of azimuths and applyinga polar-to-Cartesian coordinate transformation to each azimuth. Eachazimuth is then stored as line of data within the polar store forsubsequent processing. In this example, one line of data corresponds to1×4096 8-bit values, i.e. a rectangle of size 1×4096. For optimumprocessing, the polar store is selected to be 4K lines deep, i.e.4096×(1×4096) data lines.

When using a 4K by 4K polar store, approximately 480 scan rotations canbe processed per minute (i.e. 480 rpm), while a 16K by 16K polar storewill allow approximately 30 rpm. Higher resolution (e.g. 64K by 64K) mayfurther be used but the processing demands begin to appreciably diminishthe output of the GPU 26 on most existing cards. However, it is expectedthat the next generation of graphics cards will be able to support muchhigher processing speeds and thus all future speed increases aretherefore consistent with the method of the present invention.

It is found that a 4K by 4K polar store conversion typically requiresaround 5% of the CPU's processing power, while the rest of theprocessing is performed by the GPU 26. Hence, it is evident that thepresent implementation significantly reduces the burden on theworkstation's CPU 22, which avoids diminishing the performance of theworkstation 14 when displaying images to the operator.

The radar display system 10 of FIG. 1, applies an azimuth filter incombination with a ‘highest wins’ filter to achieve a cross-azimuthfiltering of the radar data in the polar store. The azimuth filter isapplied across adjacent azimuths as a convolution filter having aGaussian profile. Each azimuth is selected in turn, along with the twoazimuths on either side of the selected azimuth (i.e. 5 in total). Byconvolving the azimuths with the Gaussian profile, this techniqueeffectively combines the respective contributions of each of the returnsignals of any targets that are present within those azimuths. In thisway, the overall return signal is accentuated, which mitigates againstthe effect of background noise, thereby effectively boosting thesignature of the target signal. Thus, it is found that a much improvedrepresentation of the target can be reproduced within the radar image.

In the example of FIG. 1, the convolution is achieved by way of apurpose written GLSL shader operation that makes use of the standardOpenGL blend modes. The shader samples each set of azimuths (hence, datalines in the polar store) and performs azimuth filtering to convolve theazimuths with the Gaussian profile. A total of 5 azimuths is found to beoptimum for the filtering process based on existing graphics cards. Alarger number of azimuths may be processed but as the filtered areaincreases so too do the demands on the GPU 26. Hence, to avoidsignificant delays in the processing pipeline it is preferred to usesmaller samples of azimuths.

Of course, as GPU processing power increases in the future, largerfilter samples may be used in accordance with the method of the presentinvention, depending on the particular arrangement and desired filteringresult.

During the conversion of the images into data lines within the polarstore, the GPU 26 applies a mapping function that maps each pixel withinthe image to a respective byte in one or more of the data lines. Sincetargets will generally extend across several azimuths, any particularpixel in the image may therefore be associated with one or more bytes inthe polar store. The highest wins filter makes use of this pixel mappingin order to strengthen the return signal from smaller targets or targetsgiving rise to weaker return signals (e.g. highly absorbing surfacesetc.). The GPU 26 is therefore programmed via a shader to perform ahighest wins filtering process on the azimuth sample selected by theshader. The shader can make use of the same sample as selected for theazimuth filtering (discussed above) or may select another sample. Ineither case, it is found that 5 azimuths are again optimum for thisfiltering process, however the technique can also be successfullyimplemented using only 3 azimuths, and is also achievable using only 2azimuths. In the example of FIG. 1, the GPU 26 is programmed to process5 azimuths for both the azimuth and highest wins filtering.

The highest wins filter operates by identifying the highest valued bytefrom among each of the values of the bytes associated with a particularpixel within the radar image. The value assigned to that pixel is thenthe highest valued byte. In this way, any return signal is consequentlystrengthened by representing the target by the highest available pixelvalue, thereby boosting its apparent significance within the radarimage. As a result, weaker return signals may therefore be preserved andbetter distinguished over the background noise, which thereby permitseasier identification of the target within the radar image.

Once the images have been filtered according to the cross-azimuthfiltering technique, they are then displayed in real-time to theoperator via the monitor 16 of workstation 14.

To render images to the display, the GPU dynamically calculates aplurality of textures, each texture being an object that corresponds toa respective data line within the polar store, e.g. a rectangle of size1×4096 8-bit values. Depending upon the particular display mode, anynumber of textures may be rendered by the GPU to generate some part, orthe whole, of the radar image data within the polar store. The actualtextures that are rendered to the display screen will depend upon theparticular projected viewing angle and/or current zoom level, as forexample, a single data element in the polar store may be subject to azoom level that requires the element to fill the entire screen. In thisway, the texture formed by the GPU would be scaled in such a way thatonly that data element was displayed.

In the example of FIG. 1, the operating system of workstation 14 permitswindowing operations. Suitable operating systems therefore includeMicrosoft Windows, AppleMac O/S and Unix/Linux platforms running XWindow managers etc. As a result therefore, the radar images may bedisplayed within one or more dedicated windows within the operatingsystem environment of the monitor 16.

To enable the operator to control how the radar images are displayed, agraphical user interface (GUI) is provided that is installed within theoperating system of the workstation 14. This GUI is implemented as a Capplication on a Linux platform using a platform independent GTK, whichprovides real-time control of the different display modes that may beapplied to the radar images. Hence, in this way, specific shaderoperations can be invoked to achieve any particular visual effect ordisplay mode. However, the GUI may alternatively be implemented in anysuitable language that supports bindings to libraries required toaddress the underlying graphics hardware, e.g. C++, Python, Java, Ruby,C# etc.

Referring now to FIG. 2, there is shown an example screenshot of a radarimage 30 generated according to the method of the present invention. Theradar image 30 is displayed according to one of the selected displaymodes that may be directly controlled by the GUI. In this example, theradar image 30 is shown as a 2-dimensional plan view (i.e. as seen fromabove) as conventionally displayed by a CRT display screen. The radarimage 30 comprises an underlay image 32 in the form of a bitmap thatincludes a circular grid 34 of concentric circles having radial segments36. The grid 34 is centered on the point of origin 38 of the radarsignals, which corresponds to the site of the antenna 12.

The underlay image 32 also includes the outline of the coastlines 40 ofthe land masses within the monitored area. Although not shown in thegrayscale image of FIG. 2, the land masses may be contrastingly coloredin relation to bodies of water, such as lakes, seas or oceans etc. InFIG. 2, the coastlines 40 have been indicated by a contrasting color tothat of the background and therefore appear as darker lines.

Of course, it is to be appreciated that the underlay image 32 isspecific to the particular region that is being monitored by the radardisplay system and hence, the underlay image will change depending onthe location of the antenna 12. The color rendition of the underlay canhowever be controlled by the GUI, so that it may be switched between dayand night modes etc. to emulate hours of sunshine and darkness forinstance.

According to some display modes, the underlay image 32 can also beupdated so that if the point of origin (i.e. radar source) moves, suchas in arrangements where the radar is mounted on a moving vehicle, theunderlying features change. In this way, a rendered coastline or landmass, for example, can be updated as the source passes by.

The GPU 26 overlays the radar data on top of the underlay image 32, sothat any targets 42 within the monitored area are displayed within thegrid 34. The cross azimuth filtering of the azimuths results in improvedtarget definition and consequent rendition within the image. Hence, thetargets within radar image 30 are better defined, with weaker returnsignals being effectively boosted. As shown in FIG. 2, a large number oftargets 42 have been identified within the grid 34, which includes bothstronger and weaker return signals (for instance, compare tracesindicated by 44 and 46).

Therefore, it is evident that the present method provides significantadvantages in identifying weaker signals and consequently enhances thesafety of air/sea/land vehicles traversing the monitored area. Moreover,in surveillance applications the boosting of weaker signals enables anoperator to identify smaller vehicles or projectiles etc. which may posea threat to the security of the monitored area and/or other vehicles.

The GPU 26 is also responsible for rendering the sweeping radial arm 48that rotates synchronously with the antenna 12. Again, this feature isrendered in a contrasting color to that of the background and targetswithin the image 30.

The GUI allows the radar images to be manipulated and controlled toachieve any number of visual display effects according to numerousdifferent display modes. Therefore, as shown in FIG. 3, the projectedorientation (i.e. viewing angle) of the radar image 30 can be adjustedin real-time, so that the GPU 26 can render the image according to anydesired viewing angle. In this way, the radar image 30 can be impartedwith a sense of depth, with some targets 42 appearing as foregroundobjects and others appearing as background objects.

Another useful feature that the GUI permits is that specific regionswithin the grid 34 can be selected for further scrutiny, as indicated bythe arcuate section 50, which allows an operator to then zoom in on thisregion to monitor any desired targets and/or other activity.

According to another display mode, the operator has the opportunity toview multiple images and/or selected regions by way of a multi-segmentwindow, as shown in FIG. 4. In this example, the radar image 30 of FIG.2 can be re-sized and positioned within a portion (a) of themulti-segment window, while various other related aspects of the imagecan be selected for closer scrutiny. Hence, for example, a projectionplot (b) can also be drawn that allows the operator to simultaneouslyhave both a plan view and an angled view of the monitored area. One ormore regions may also be selected, as shown in (c), when it is desiredto track a particular target 42 as it traverses the monitored area. Inthis way, an operator can still keep his attention on the whole area,while also monitoring a particular target in more detail.

It is also possible to zoom in on particular targets or scan regions anddisplay the results within separate dedicated portions within themulti-segment window, as shown in (d), where for example, the bottomplot is a 3-dimensional rendered image of three targets of interestwithin the image drawn in (a).

An operator may also inspect any line of data within the polar store asa suitable line graph, as shown in portion (e) as the ‘A-scan’, or zoomin on this graph (i.e. a ‘Zoomed A-Scan’) as illustrated by portion (f),to scrutinize any particular point of interest.

Hence, it is to be understood that the GUI allows any number ofcombinations of different display modes, either within a singlemulti-segment window or multiple separate windows, each with real-timeupdates and monitoring, and permitting resizing of the windows asdesired.

As an example of the 3-dimensional rendering of targets within theimages, FIG. 5 illustrates a section selected for further scrutiny, inwhich two targets have been drawn with a rendered depth perception. Suchrendering can assist an operator in identifying targets and may also beuseful in determining particular vehicle profiles, as the renderedtraces may give some indication as to what the target actually is. Anytarget within the radar image 30 may be selected and drawn in this way,permitting an operator to better scrutinize identified targets.

Such functionality is clearly not possible with existing CRT displaysystems, and therefore the present implementation offers significantadvantages in visualization of the data, which therefore makes best useof the radar information.

A fading effect is implemented by way of a shader operation in thegraphics pipeline that emulates the persistence of a CRT phosphorscreen. Therefore, as shown in FIG. 6, targets 42 can be rendered suchthat they leave a trail 52 in successive images as they traverse themonitored area. Hence, by action of the shader, a particular target willleave a streaked trail 52 as it moves between images, which thereby canassist the operator in determining the header and/or velocity of thetarget 42. As shown in FIG. 6, some targets 42 are found to be movingtangentially to the point of origin 38, while others are moving radiallytowards/away from the point of origin 38.

The present implementation is also able to merge more than one radarimage set. Therefore, should two or more monitored areas overlap (e.g.arising from multiple sources), the radar data from each PPI can bedisplayed within the same display window. In such arrangements, theworkstation 14 is provided with each respective radar signal feed, whichafter digitisation and processing can be displayed as a single imagehaving overlapping range and azimuth grids. Each grid and associatedtargets can be coloured differently between the two or more PPIs, and ashader operation can be invoked to alter the displayed colors where theradar traces overlap/intersect.

Illustrative embodiments have been described, hereinabove. It will beapparent to those skilled in the art that the above devices and methodsmay incorporate changes and modifications without departing from thegeneral scope of this invention. It is intended to include all suchmodifications and alterations within the scope of the present invention.Furthermore, to the extent that the term “includes” is used in eitherthe detailed description or the claims, such term is intended to beinclusive in a manner similar to the term “comprising” as “comprising”is interpreted when employed as a transitional word in a claim.

1. A method of generating a radar image to be displayed by a radarsystem, said method including: receiving range data and azimuth datacarried by a radar signal transmitted from a radar antenna incommunication with the radar system, wherein the range data and theazimuth data represent the radar image as a plurality of azimuthsegments that collectively form the radar image in a polar coordinatesystem; translating the range data and the azimuth data into abscissadata and ordinate data that represent the radar image in a Cartesiancoordinate system; filtering noise from the radar image by: utilizing areturn signal contribution reflected by a target from at least twoimmediately-adjacent azimuth segments to render a representation of thetarget in the radar image, selecting a highest pixel value from aplurality of different pixel values assigned to be displayed by a commonpixel of a radar display to be displayed by the common pixel, or acombination of both utilizing the return signal contribution reflectedby the target from the at least two immediately-adjacent azimuthsegments and selecting the highest pixel value from the plurality ofdifferent pixel values assigned to the common pixel to render therepresentation of the target to be included as a portion of the radarimage to be displayed; and generating the radar image including thetarget to be displayed by a display screen to an operator.
 2. The methodaccording to claim 1 further including converting the radar signal feedfrom an analog signal to a digital signal.
 3. The method according toclaim 2, wherein converting the radar signal to a digital signal isperformed by an analog-to-digital converter provided to a graphicsprocessing unit of the radar system independent of a central processingunit for controlling general operation of the radar system as a whole.4. The method according to claim 1, wherein translating the range dataand the azimuth data into abscissa data and ordinate data, filtering thenoise from the radar image, or both translating the range data and theazimuth data into abscissa data and ordinate data, and filtering thenoise from the radar image is performed by a graphics processing unit ofthe radar system independent of a central processing unit forcontrolling general operation of the radar system as a whole.
 5. Themethod according to claim 1, wherein one of translating the range dataand the azimuth data and filtering the noise from the radar image isperformed by a graphics processing unit of the radar system independentof a central processing unit for controlling general operation of theradar system as a whole, and another of translating the range data andthe azimuth data and filtering the noise from the radar image isperformed by a different processing unit provided to the radar system.6. The method according to claim 5, wherein the different processingunit is the central processing unit for controlling general operation ofthe radar system as a whole.
 7. The method according to claim 1 furtherincluding transmitting the radar image over a communication network tobe displayed by the display screen.
 8. The method according to claim 1further including storing range data and azimuth data representing theplurality of azimuth segments that collectively form the radar image asan array in a computer-readable memory.
 9. The method according to claim1 further including manipulating a point of view of the radar image tobe displayed by the display screen in at least one of a first dimensionand a second dimension responsive to receiving an input from theoperator indicating a desired viewpoint of the radar image.
 10. Themethod according to claim 9, wherein manipulating the point of view ofthe radar image further includes adjusting an orientation of the radarimage in a third dimension.
 11. The method according to claim 9, whereinmanipulating the point of view of the radar image further includesconducting a geometric distortion to maintain substantially-overheadpoint of view of the radar image subsequent to manipulating the point ofview.
 12. The method according to claim 1 further including generating aplurality of different points of view of the radar image to besimultaneously displayed by the display screen.
 13. The method accordingto claim 1 further including displaying the radar image over andunderlay image representing a reference point of a target in the radarimage.
 14. The method according to claim 1, wherein the target is to bedisplayed as a graphical depiction of the target in real time by pixelsof the display screen, the method further including gradually fading anintensity of the pixels displaying the target in the radar image toemulate a persistence of phosphor of a cathode-ray-tube display screen.15. The method according to claim 14, wherein gradually fading theintensity of the target in the radar image is controlled by a graphicsprocessing unit of the radar system independent of a central processingunit for controlling general operation of the radar system as a whole.16. The method according to claim 1, wherein a plurality of the azimuthsegments collectively forming the radar image overlap to each detect atarget in a common region.
 17. The method according to claim 16, whereinfiltering noise from the radar image includes comparing a return signalcontribution reflected from the common region for each overlappingazimuth segment, and generating the radar image to include the targetwithin the common region if each return signal contribution isindicative of a presence of the target within the common region.
 18. Aphysical computer-readable medium storing computer executableinstructions for performing the method of claim
 1. 19. A radar systemincluding: a radar antenna for transmitting an outgoing signal andreceiving a return signal contribution reflected by a targetinterrogated by said outgoing signal; an analog-to-digital converter forconverting a radar feed signal transmitted from the radar antennacommunicating the return signal contribution reflected by the target; acomputer-readable memory for storing, at least temporarily, an array ofrange data and azimuth data carried by the radar feed signal, whereinthe range data and the azimuth data represent the radar image as aplurality of azimuth segments that collectively form the radar image ina polar coordinate system; a radar scan converter for translating therange data and the azimuth data into abscissa data and ordinate datathat represent the radar image in a Cartesian coordinate system; afiltering component for filtering noise from the radar image by:utilizing the return signal contribution reflected by the target from atleast two immediately-adjacent azimuth segments to render arepresentation of the target in the radar image, selecting a highestpixel value from a plurality of different pixel values assigned to bedisplayed by a common pixel of a radar display to be displayed by thecommon pixel, or a combination of both utilizing the return signalcontribution reflected by the target from the at least twoimmediately-adjacent azimuth segments and selecting the highest pixelvalue from the plurality of different pixel values assigned to thecommon pixel to render the representation of the target to be includedas a portion of the radar image to be displayed; a graphics processingunit for generating the radar image including the target to bedisplayed; a display screen for displaying the radar image generated bythe graphics processing unit to an operator; and a central processingunit for controlling interactions among radar system components.
 20. Theradar system according to claim 19, wherein the graphics processing unitincludes a programmable pipeline and generates the radar imageindependent of the central processing unit.
 21. The radar systemaccording to claim 19, wherein the filtering component includes aphysical computer-readable medium storing computer-executable logic tobe executed for filtering noise from the radar image.
 22. The radarsystem according to claim 21, wherein execution of thecomputer-executable logic performs a Gaussian convolution with thereturn signal contribution reflected by the target to minimize noise inthe radar image.
 23. The radar system according to claim 19, wherein thegraphics processing unit includes one or more of: the computer-readablememory for storing, at least temporarily, an array of range data andazimuth data carried by the radar feed signal; the radar scan converter;and the filtering component.